The present invention relates to a metal-insulator-semiconductor-field-effect transistor (MISFET) and a semiconductor device comprising a metal-insulator-semiconductor-field-effect transistor.
The integrated circuit technology using silicon has been developed at an amazing speed. As a miniaturization technology progresses, the size of the devices has been reduced, it has become possible to integrate an increasing number of devices in a single chip, and, as a result, an increasing number of functions have been realized. At the same time, a higher operation speed has been achieved by enhancement of drive current capability and a reduction in parasitic capacitance with the miniaturization of the devices.
The enhancement of the drive current capability of the field effect transistor is due mainly to thinning of the gate dielectric film. Even if the gate dielectric film is made thinner, the power source voltage is not lowered proportionately. Therefore, a very high electric field has come to be impressed on an inversion layer. Further, the increase in the impurity concentration in a channel so as to restrain a short channel effect attendant on the miniaturization of devices also spurs the rise in electric field. When a high electric field is applied to the inversion layer, carriers are scattered due to the roughness of the interface between the silicon substrate and the gate dielectric film (hereinafter, referred to simply as “the substrate surface roughness”), so that there is the problem that mobility is lowered. The same degree of roughness is present not only at the interface between the silicon substrate and the gate dielectric film but also at the interface between the gate dielectric film and a gate electrode. The variation in the thickness of the gate dielectric film will be referred to simply as “the gate roughness”.
In view of the above, many researches on reduction in the substrate surface roughness have been made. For example, Japanese Patent Laid-open Nos. 5-343391 (1993), 9-158543 (1997), and 2000-235975 describe methods of forming an oxide film by use of radical oxygen. Japanese Patent Laid-open No. 10-223888 (1998) describes a method of alleviating the substrate surface roughness by use of a film stack of a pyro-oxide film and a dry-oxide film, and Japanese Patent Laid-open No. 11-176828 (1999) describes a method of removing a spontaneous oxide film, thereafter providing a low temperature oxide film as a protective film, and then performing an oxidation process.